1. Field of the Invention
This invention concerns a method for tolerating a breakdown and/or a decoupling of at least one network node in, e.g. from a communication network. This is used for controlling and/or adjusting the movement of a plurality of machine parts, for example rotation bodies in printing, machines, machine tools, or other production machines. The network is operated accordingly as a closed, single or multiple ring structure. The term “multiple ring structure” is to be understood to mean redundant ring structures such as double rings as well as the decoupling of several independently closed ring (part) networks. Within the network each node communicates by means of a first receiver or port with a transmitter or port of a first adjacent node, and by means of a second transmitter or port with a receiver or port of a second adjacent node. During the breakdown or decoupling of at least one of the nodes the closed ring structure is maintained. The invention further concerns a data path switching device suitable for carrying out the method, which incorporates internal input and output side data connection means, a multi-port connection means for the communication technical connection of a plurality of network nodes, network or field bus segments, separate networks and/or other network configurations as well as a communication network, structured and organised according to a single or multiple ring topology, with which a plurality of network nodes, network or field bus segments, separate networks and/or other network configurations are coupled.
2. Description of the Related Art
With process automation networks there exists the tendency of integrating data transmission protocols from the office and Internet world. New standards for driver interfaces such as SERCOS III and EtherCAD have contributed to this, where elements of the network type “Ethernet” from the office environment are used under real time conditions (so-called “Real Time Ethernet Field Bus”). For tolerating the breakdown of individual nodes (“single breakdowns”) these communication systems are equipped with double ring structures, where two independent communication channels enable opposite ring transmissions. This results from Ethernet physics. Due to the therefore redundant data transfer the communication capability is preserved completely at any point of the ring during a cable break or a user/node breakdown. The interruption of the ring structure is in fact limited to the location of the breakdown. When a line breakdown and/or a node breakdown occurs the communication master will still be able to control the ring sections located to both sides of the location of the breakdown and interruption.
However, if two separate, e.g. spatially distant ring sections of the known communication double ring described above break down, the users/nodes of the communication system between the broken down or even switched off sections are no longer accessible via the ring to the communication master or another controller.
A data transmission system for machine tools and production machines as well as robots is known from EP-B-1 249 763 (Siemens AG). From a central data line other data lines, in which signal processing units with transmitters and receivers are located, branch off at intervals. The latter serially transmit the data within a ring structure. Individual ring networks are each controlled by a communication master, which are in turn compiled into a closed separate ring structure, so that a breakdown of a communication master will not result in the entire communication structure breaking down. The communication masters are supported by standby communication masters, which are coupled with adjacent communication masters via additional lines installed according to the by-pass principle. If one communication master with a group leader function breaks down, the standby communication masters will guarantee that a ring-shaped part communication structure will continue to function. The standby communication master will seamlessly take over the group leader function in this case, and will dominate the signal processing units of the associated part communication ring. With the aid of the additional connections (by-pass lines) the relevant broken down communication master is bridged. However, these data, e.g. communication by-pass lines will result in a clearly increased and confusing hardware requirement. In addition there is no prevention mechanism guarding against a multiple breakdown or switch-off of subordinate slave signal processing nodes.
In DE-A-101 29 572 (Siemens AG) a data path selection means with a plurality of data connections for a wired data transmission system is described. Any number of data connections can be located between the data connections of the data path selection means. Communication networks can be coupled with other communication networks in this way. The use of real time enabled Ethernets for ring-shaped networked drive controllers is also mentioned. If one machine unit and/or the drives of the same break down, the same can be decoupled from the data communication by means of the data path selection means. For this a data technical re-allocation of the remaining signal processing units/drive controllers to associated machine parts within the overall control network is carried out by means of the data selection means.